In the fabrication process of electronic devices, for instance, integrated circuits (ICs), it is essential to detect defects effectively at an early stage in order to maintain and improve yield rates. Charge particle beam systems such as electron beam inspection (EBI) systems, are being widely implemented in in-line defect monitoring. EBI systems are able to detect electrical failures such as open and leakage defects through the use of voltage contrast (VC).
Image comparison techniques are commonly used for defect detection in IC manufacturing processes. Typically, charged particle microscope images for a “defect site” and a “reference site” are acquired. Every image comprises a plurality of pixels, with each pixel being defined by its location within the image. The two images are aligned pixel-by-pixel. Pixel grey level variations are then obtained by comparing or subtracting their surface charge induced grey levels or intensities. Grey level value (GLV) is determined by taking the maximum GLV from the “defective site” pixels. For some defects, for example, leakage defects which cause bright voltage contrast (BVC), the real GLV can be distorted by surrounding charging effects or noises, resulting in inaccurate and inconsistent GLV based on one pixel. Therefore, challenges for charge particle beam inspectors to distinguish killer and non-killer defects exist.